It is now four games without a win for Manchester City and Pep Guardiola and questions will be asked.
Manchester City traveled to Camp Nou hoping to get a respectable result against Barcelona but ultimately, they were well beaten.
To be fair, all the mistakes were theirs. They started brightly albeit with Kevin De Bruyne playing as a false nine while Sergio Aguero looked on from the bench.
City quickly went behind after an uncharacteristic mistake by Fernandinho allowed Messi to round Bravo and open scoring.
City wasted precious chances to possibly draw level and if there was any hope of drawing level, Claudio Bravo effectively ended it.
The ball playing goalie handled the ball outside the box after misplacing a pass and he was given his marching orders.
Playing Barca with a man down is no mean feat and City will now know this firsthand. Messi was then left unmarked at the edge of the box and he dispatched his shot past Caballero for his brace.
His hat trick came thanks to another error from John Stones who did not anticipate a back pass and let Messi bag his hat trick.
City then conceded a penalty which Neymar missed before making up for it by scoring the fourth goal.